It has long been a challenge in manufacturing, inspection, and assembly applications to more precisely and accurately position the tool or probe of a machine with respect to a workpiece, such that part errors may be determined or predicted and minimized or eliminated. This challenge is most acute when a manufacturing, inspection, or assembly process is carried out in the presence of environmental variations, such as thermal variations in a manufacturing or assembly facility or those associated with open-bay machining applications. Problems may also be encountered when tight or nanometric tolerances are required, such as those associated with micro-electromechanical systems (MEMS) applications or micro/nano-electronics applications, and when large parts are being manufactured, inspected by measurement, or assembled, such as in aerospace applications.
Manufacturing, inspection, and assembly machines typically include a controller capable of specifying a part coordinate system rigidly defined with reference to the coordinate system of the machine. This may be accomplished through, for example, linear and/or rotational transformation of the coordinates. As a result, the part coordinate system is only as precise and accurate as the underlying machine coordinate system. As discussed above, both the workpiece or part and the machine are subject to thermal and structural variations. These variations may alter the real position of the tool or probe with respect to the workpiece during the manufacturing, inspection, or assembly process, resulting in real part errors, measurement errors during inspection, or assembly alignment errors.
There have been a number of attempts to overcome these challenges and to control or correct these problems, many of which are specific to a particular manufacturing or assembly process. Typically, these systems and methods involve measuring the geometric errors associated with a given machine or tool and/or the relative position of a workpiece. Corrections are then made to command the position of the machine or tool to manufacture a part within predetermined tolerances.
Various United States patents disclose such conventional systems and methods. For example, U.S. Pat. No. 5,428,446 discloses a laser interferometry-based ball bar test gauge for use in spatial dimensional metrology applications. In another example, U.S. Pat. No. 5,903,459 discloses a machine control and product acceptance method augmented by external measurement feedback. The positions of a tool holder and a workpiece are measured using a laser tracker and compared to generate a machine correction code. U.S. Pat. Nos. 5,920,483 and 5,949,685 disclose the use of an interferometric laser tracker or other three-dimensional position sensor to monitor part shape and to measure machine changes due to thermal variations. Machine position corrections are made via trickle feed media statements. U.S. Pat. No. 4,780,617 discloses a semiconductor device manufacturing method by which the alignment of a substrate within an exposure apparatus is corrected via the measurement of a plurality of marks. Orientation, rotation, and expansion errors associated with the wafers are part of the realignment calculation. Positions and errors are measured, corrected, and commanded utilizing the position coordinates of steppers. U.S. Pat. No. 4,833,621 discloses another substrate alignment method and apparatus with a reticule facilitated by measuring multiple reference areas and statistically averaging the areas. The average areas are used to more precisely and accurately position the wafer under the reticule for exposure. U.S. Pat. No. 5,521,036 discloses a further positioning method and apparatus suitable for use with an exposure apparatus employed in a lithography process for manufacturing semiconductor elements and liquid crystal devices. Alignment is facilitated by utilizing various patterns disposed on a mask, the patterns associated with a desired chip pattern. Finally, U.S. Pat. No. 5,610,102 discloses a method for co-registering semiconductor wafers undergoing work in one or more blind process modules. Mounting techniques are utilized in conjunction with pattern recognition and flexures for adjustment.
What is still needed are fiducial calibration systems and methods that reference machine positioning metrology directly to the current state of a workpiece, while extricating the positioning metrology from the current state of the manufacturing or assembly machine. What are needed are systems and methods that allow for a reduction in manufacturing errors, including those errors that are unpredictable, immeasurable, and changing. What are also needed are systems and methods that allow manufactured parts, such as airfoils, to be assembled with critical dimensions and alignments.